It should work with all programs that load RICHED20.DLL directly. For programs that load RICHED32.DLL you need a native version of that DLL (which is a wrapper for RICHED20.DLL, providing compatibility with 1.0 version of the control, the most important thing it does is loading RICHED20.DLL, which registers 2.0 window classes).
http://foltman.com/riched20.tar.gz http://foltman.com/richeditpatch.diff
Note, that EM_STREAMIN and EM_STREAMOUT don't work, so if your program uses RTF to insert text to the control, it won't work !
WinXP WordPad doesn't work either, as it uses RICHEDIT50W window class (what I provide is RichEdit20W control, haven't tried to fake it's 5.0).
Have fun!
Krzysztof